1. Field of the Invention
The present invention relates to a communication system, and more particularly, to a method of processing bandwidth recovery of a communication system.
2. Description of the Prior Art
With wireless technology becoming more and more popular, related standards such as IEEE 802.16 have been established. A major objective of IEEE 802.16 Broadband Wireless Access Standard is to solve problems associated with “last mile”; IEEE 802.16 Broadband Wireless Access Standard supplies a wireless transmission technology for replacing conventional wired transmission technology of long distance that utilizes cables or digital subscriber loops (DSL).
Different from the wireless accessing technology established by the IEEE 802.11 standard, IEEE 802.16 applies a scheduling algorithm upon the media access control (MAC) for distributing wireless resources to a plurality of Subscriber Stations (SS). According to the IEEE 802.16 standard, a transmission time is divided into a plurality of frames each having a fixed size. In addition, each frame is further divided into a downlink subframe (DL subframe) and an uplink subframe (UL subframe). Please note, however, that the size of the DL subframe is not restricted to be the same as that of the UL subframe.
In the DL subframe, the communication traffic between a base station (BS) and subscriber stations downloads data from the base station to the subscriber stations; in the UL subframe, the communication traffic between the base station and subscriber stations uploads data from the subscriber stations to the base station.
At the beginning of the DL subframe, there is a short message acting as an uplink scheduling message, also named as UL-MAP in accordance with the IEEE 802.16 standard. The uplink scheduling message is generated from the base station, and includes message transmission scheduling of the subscriber stations. That is to say, the base station uses the uplink scheduling message to schedule the timing when the subscriber stations are allowed to transmit data to the base station, to schedule the data amount to be transmitted when the subscriber stations are granted to transmit data to the base station, and then the base station broadcasts the uplink scheduling message to the belonging subscriber stations.
In some specific conditions (detailed below), the uplink channel will become idle, resulting in the waste of bandwidth.
1. Idling UL-Burst Period Problem
When a noise interference source approaches the BS, the information carried within the uplink scheduling message will be damaged. All the subscriber stations of the BS consequently fail to receive the uplink scheduling message correctly and therefore the subscriber stations lack the information for uploading data to the BS. In other words, the subscriber stations have no idea of when to upload data. As a result, the whole UL-burst period is idle due to no subscriber station being capable of uploading data, causing an excessive waste of the bandwidth.
2. Uplink Hole Problem
The uplink hole problem happens when a noise interference source approaches some of the subscriber stations, making the affected subscriber stations fail to receive the information carried within the uplink scheduling message correctly. If the uplink scheduling message contains information for informing the subscriber stations of the timing when to upload data, the intervals originally scheduled within the UL-burst period for the subscriber stations interfered by the noise interference source will become idle, resulting in waste of the bandwidth.
3. Padding Waste Problem
In accordance with the IEEE 802.16 standard, if the base station schedules an uplink time longer than the subscriber station actually requires for uploading data, the subscriber station will transmit padding data (such as padding bits or padding MPDU) to the base station for filling the remaining uplink time. Sometimes, the size of the padding data is up to 2041 bytes, causing serious waste of uplink channel bandwidth.
The IEEE 802.16 standard does not currently deal with the aforementioned three problems. Therefore, a bandwidth recovery method for solving the aforementioned bandwidth waste problems is desired.